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New blood test to detect Down syndrome

A highly accurate prenatal test for Down syndrome involving a simple blood test has been developed in Hong Kong, with the hope it may one day lessen the need for invasive and riskier tests like amniocentesis.

While it’s not yet available in Australia – and is unlikely to be for a while – the test has been found to be 99.1 percent accurate in detecting Down syndrome.

The test, which uses state-of-the-art DNA sequencing technologies to detect Down syndrome in unborn babies by directly analysing a blood sample from the mother, can reduce the use of invasive prenatal tests by 98 percent.

Developed by The Chinese University of Hong Kong, the test is already being used in Hong Kong, in mainland China and the US.

Pros and cons

Lead researcher, Professor Rossa Chiu, who trained at Queensland University, outlines the main benefits of the test.

“It is completely safe and harmless to the unborn child. The test has very high detection rates with very low false-positive rates. It can be done from the 10th week of pregnancy and is not restricted to any particular gestational age period,” she says.

But, Professor Chiu admits it has one key disadvantage – cost.

“The state-of-the-art DNA sequencing and bioinformatics analysis require a high capital outlay,” she says. “The cost of the test is around US$1000 to US$2000.”

About the syndrome

Down syndrome, affects about one in 800 pregnancies, and is caused by the presence of an additional copy of chromosome 21 in the genome of affected individuals. It causes a range of intellectual and developmental difficulties.

The risk of having a baby with Down syndrome increases with the age of the pregnant woman. For example, when a woman is 40 years old, the risk is one in 60, compared with one in 1500 when she is 25 years of age.

Down syndrome is conventionally diagnosed by analysing genetic material obtained directly from the foetus through invasive procedures such as amniocentesis and chorionic villus sampling (CVS). Both of these carry a miscarriage risk of about one percent.

Non-invasive screenings, in the form of ultrasounds, blood tests and combination of both, are also available but they can't show for certain that a baby has Down syndrome – they just provide a risk factor. Many women in Australia now will undergo these screenings in their first or second trimester.

Pregnant women who show a high risk factor – usually determined as one in 300 – may be counselled about whether they want to have one of the more invasive tests. About one in 20 women will have an “increased risk” result, but it’s worth noting that most go on to have a baby that is not affected by Down syndrome.